Philip K. Dick 
Piper in the Woods [PDF ebook] 

Under extreme duress, the human mind can come up with an array of impossibly complex coping mechanisms. Is that what’s behind the strange epidemic that army physician Henry Harris has noticed overtaking soldiers who have returned from the distant celestial body known as Asteroid Y-3? Harris makes a trip to the asteroid to figure things out — and seems to fall prey to the ‘delusion’ himself. Fans of Philip K. Dick’s unique brand of suspenseful science fiction will love this twisted tale.